default-map

Map with default value

~~~js
import {DefaultMap} from "@hoge1e3/default-map";
import * as assert from "assert";
// Map with default value is 0
const m=new DefaultMap(0);
m.set("foo",5);
assert.equal(m.get("foo"),5);
// key 'bar' is missing. get("bar") returns the default value
assert.equal(m.get("bar"),0);

// The default value is set by function that receives the missing key.
const n=new DefaultMap((k)=>Unknown '${k}');
n.set("foo","I know the foo.");
assert.equal(n.get("foo"),"I know the foo.");
// key 'bar' is missing. get("bar") generates default value and the value is associated to the key 'bar'
assert.equal(n.get("bar"),"Unknown 'bar'");
// The value can be overriden;
n.set("bar","I also know the bar.");
assert.equal(n.get("bar"),"I also know the bar.");

// Default value with mutable object, setEmpty should be true
const o=new DefaultMap(()=>[], true);
// o.get("cat") calls o.set("cat",[]) automatically.
const cats=o.get("cat");
cats.push("Persian");
cats.push("Bengal");
cats.push("Ragdoll");
const dogs=o.get("dog");
dogs.push("Bulldog");
dogs.push("Chihuahua");
// If setEmpty==false, the o.get("cat") will be empty array!
assert.deepStrictEqual(o.get("cat"), ["Persian","Bengal","Ragdoll"]);
assert.deepStrictEqual(o.get("dog"), ["Bulldog","Chihuahua"]);
// If setEmpty==false, o.has("cat") never true until o.set("cat",...) is called
assert.ok(o.has("cat"));
assert.ok(o.has("dog"));
assert.ok(!o.has("rabbit"));
~~~

API

- DefaultMap extends Map
- new DefaultMap(def:V|(key:K)=>V, setEmpty=false)
- Create DefaultMap
- def a default value or function that returns value for given key
- setEmpty if set to true, when get(key) is called and the key is missing, the default value (given by def) is set to the key, otherwise, the default value is not set.
- setEmpty should be true if the associated value is a mutable object(such as array).